A new stationary phase for reversed-phase high performance liquid chromatography (RP HPLC) was created by coating spherical 3 μm carbon core particles in a layer-by-layer (LbL) fashion with poly(allylamine) (PAAm) and nanodiamond. Unfunctionalized core carbon particles were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and Raman spectroscopy. After LbL of PAAm and nanodiamond, which yields ca. 4 μm core-shell particles, the particles were simultaneously functionalized and cross-linked using a mixture of 1,2-epoxyoctadecane and 1,2,7,8-diepoxyoctane to obtain a mechanically stable C(18)/C(8) bonded outer layer. Core-shell particles were characterized by SEM, and their surface area, pore diameter, and volume were determined using the Brunauer-Emmett-Teller (BET) method. Short stainless steel columns (30 × 4.6 mm i.d.) were packed and the corresponding van Deemter plots obtained. The Supporting Information contains a MATLAB program used to fit the van Deemter data. The retentions of a suite of analytes were investigated on a conventional HPLC at various organic solvent compositions, pH values of mobile phases, including extreme pH values, and column temperatures. At 60 °C, a chromatogram of 2,6-diisopropylphenol showed 71,500 plates/m (N/m). Chromatograms obtained under acidic conditions (pH 2.7) of a mixture of acetaminophen, diazepam, and 2,6-diisopropylphenol and a mixture of phenol, 4-methylphenol, 2-chlorophenol, 4-chlorophenol, 4-bromophenol, and 1-tert-butyl-4-methylphenol are presented. Retention of amitriptyline, cholesterol, and diazinon at temperatures ranging from 35 to 80 °C and at pH 11.3 is reported. A series of five basic drugs was also separated at this pH. The stationary phase exhibits considerable hydrolytic stability at high pH (11.3) and even pH 13 over extended periods of time. An analysis run on a UHPLC with a "sandwich" injection appeared to reduce extra column band broadening and gave best efficiencies of 110,000-120,000 N/m.

Here, we report efficiencies up to 112,000 plates per meter (a reduced plate height, h, of 2.22) for RP, carbon/nanodiamond/aminopolymer particles using conventional injection conditions in HPLC. This efficiency greatly exceeds our best previously reported value of 71,000 N/m (h = 3.52). The carbon cores used in this study were derived from carbonized poly(divinylbenzene) spheres that were either made in-house by a two-step polymerization procedure or obtained commercially. The resulting particles showed good uniformity and were oxidized in nitric acid to increase their dispersability. X-ray photoelectron spectroscopy confirms particle oxidation and subsequent aminopolymer deposition. Layer-by-layer (LbL) growth of poly(allyamine) and nanodiamond was demonstrated to produce core-shell particles. After LbL growth, the particles were functionalized, sieved, and packed into columns. The column functionalization and packing were reproducible. Van Deemter curves indicated that the commercially obtained poly(divinylbenzene) spheres outperformed those synthesized in our laboratory. The columns appear to be stable at 120°C in a pH 11.3 mobile phase. Longer columns (2.1 × 50 mm) than previously reported were packed. Four essential oils were separated by gradient elution.

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Three mixed-mode high-performance liquid chromatography columns packed with superficially porous carbon/nanodiamond/amine-polymer particles were used to separate mixtures of cannabinoids. Columns evaluated included: (i) reversed phase (C18 ), weak anion exchange, 4.6 × 33 mm, 3.6 μm, and 4.6 × 100 mm, 3.6 μm, (ii) reversed phase, strong anion exchange (quaternary amine), 4.6×33 mm, 3.6 μm, and (iii) hydrophilic interaction liquid chromatography, 4.6 × 150 mm, 3.6 μm. Different selectivities were achieved under various mobile phase and stationary phase conditions. Efficiencies and peak capacities were as high as 54 000 N/m and 56, respectively. The reversed phase mixed-mode column (C18 ) retained tetrahydrocannabinolic acid strongly under acidic conditions and weakly under basic conditions. Tetrahydrocannabinolic acid was retained strongly on the reversed phase, strong anion exchange mixed-mode column under basic polar organic mobile phase conditions. The hydrophilic interaction liquid chromatography column retained polar cannabinoids better than the (more) neutral ones under basic conditions. A longer reversed phase (C18 ) mixed-mode column (4.6 × 100 mm) showed better resolution for analytes (and a contaminant) than a shorter column. Fast separations were achieved in less than 5 min and sometimes 2 min. A real world sample (bubble hash extract) was also analyzed by gradient elution.

*We report a multi-instrument characterization of the carbon particles in carbon/polymer/nanodiamond core-shell materials used for high-performance liquid chromatography. These particles are prepared by the carbonization/pyrolysis of poly(divinylbenzene) (PDVB) microspheres. Scanning electron microscopy showed that the particles (4.9 μm initially) decreased in size after air oxidation (to 4.4 μm) and again after carbonization (down to 3.5 μm) but remained highly spherical. Brunauer-Emmett-Teller measurements showed low surface areas initially (as received: 1.6 m 2 /g, after air oxidation: 2.6 m 2 /g) but high values after carbonization (445 m 2 /g). Fourier transform infrared spectroscopy revealed the changes in the functional groups after air oxidation (C = O and C-O stretches appear), carbonization (carbon-oxygen containing moieties disappear), and acid treatment (reintroduction of carbon-oxygen containing moieties). X-ray photoelectron spectroscopy (XPS) and elemental analysis revealed the surface and bulk oxygen contents before and after treatments. By XPS, the atom percent oxygen for the as received, air oxidized, carbonized, and acid treated particles are 8.7, 16.6, 3.7, and 13.8, respectively, and by elemental analysis, the percent oxygen in the materials is 0.6, 8.1, 0.9, 16.9, respectively. A principal components analysis of time-of-flight secondary ion mass spectrometry data identified ions that were enhanced in the different materials, where almost 90% of the variation in the analyzed peak areas was captured by two principle components. X-ray diffraction and Raman spectroscopy suggested that the carbonized PDVB was disordered. Thermogravimetric analysis showed significant differences between the differently treated PDVB microspheres. This work applies directly to a commercial product and the process for preparing it.